Field effect transistors (FETs) composed of discrete silicon (Si) active regions or “fins,” referred to as FinFETs, have desirable electrostatic properties compared to planar devices. In connection with FinFETs, sublithographic line space patterning can be based on the directed self-assembly (DSA) of block copolymers (BCPs). DSA is a technique that utilizes phase separation of a BCP thin film in order to form a sublithographic line space pattern. BCP films naturally phase separate into periodic patterns with a feature size pre-defined by the molecular weights of the BCP. By combining bottom up lamellae forming self-assembling materials with top down lithographically defined template patterns, gratings at relatively small pitches can be achieved. Features, such as, for example, resolution and the critical dimension (CD) of a pattern are dependent on a composition of the copolymer used in DSA processing.
In a DSA process, phase separated copolymers can be aligned using self-assembly guided by, for example, surface topography, referred to as graphoepitaxy, and/or surface chemical patterning, referred to as chemoepitaxy. More specifically, DSA uses a template layer to cause desired alignment of phase separated polymers. For example, DSA by chemoepitaxy utilizes a chemical pattern to align a block copolymer deposited on the chemical pattern. DSA by graphoepitaxy utilizes surface topography (e.g., trenches) to align a deposited block copolymer to create desired line and space patterns.
Since the BCPs self-assemble at a certain pitch, DSA can provide relatively simple processing, compared to multiple exposures or multiple depositions and etching, and high resolution of features at small dimensions (e.g., less than 10 nm). DSA is compatible with existing lithography techniques, and allows for frequency multiplication and space subdivision.